Objective: We have shown expression and localization of gap junction protein connexin 43 (CX43) in human and rat dental pulp. In the present study, we examined expression of CX43 and heat shock protein 70 (HSP70) under heat stressed condition in rat dental pulp. Methods: Dental pulp cells were obtained from young Sprague-Dawley rat incisors and cultured from 2nd to 6th passage. The cultured cells were treated at 42ūC for 30 min, and Western blot and immunohistochemistry were carried out. Results: Western blot of total lysate and immunohistochemistry demonstrated rapid degradation of CX43 after heat treat. Western blot analysis also showed that 43 and 45kDa bands indicating slight and highly phosphorylated forms of CX43 decreased dramatically after heat treatment. However, 41kDa band representing non-phosphorylated form did not change. CX43 expression and distribution returned to normal level by 6 h following heat treatment. Furthermore, heat-induced degradation of CX43 was prevented by simultaneous treatment when inhibitors, such as lactacystin, MG132 and leupeptin, were added into culture medium prior to heat treatment. Heat shock led to production of HSP70 and the expression gradually increased, although HSP70 expression was slightly observed before heat treatment. Conclusion: These results suggest that heat stressed condition induces reduction of gap junctional communication by degradation of CX43 via both proteasomal and lysosomal pathways, and HSP70 may protect against CX43 degradation.

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